Various types of hearing prostheses may provide persons with different types of hearing loss with the ability to perceive sound. Hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural hearing loss. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Persons with some forms of conductive hearing loss may benefit from hearing prostheses, such as acoustic hearing aids or vibration-based hearing aids. An acoustic hearing aid typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a small speaker to transmit the amplified sounds into the person's ear. Vibration-based hearing aids typically include a small microphone to detect sound, and a vibration mechanism to apply vibrations corresponding to the detected sound to a person's bone, thereby causing vibrations in the person's inner ear, thus bypassing the person's auditory canal and middle ear. Vibration-based hearing aids may include bone anchored hearing aids, direct acoustic cochlear stimulation devices, or other vibration-based devices. A bone anchored hearing aid typically utilizes a surgically-implanted mechanism to transmit sound via direct vibrations of the skull. Similarly, a direct acoustic cochlear stimulation device typically utilizes a surgically-implanted mechanism to transmit sound via vibrations corresponding to sound waves to generate fluid motion in a person's inner ear. Other non-surgical vibration-based hearing aids may use similar vibration mechanisms to transmit sound via direct vibration of teeth or other cranial or facial bones.
Persons with certain forms of sensorineural hearing loss may benefit from cochlear implants and/or auditory brainstem implants. For example, cochlear implants may provide a person having sensorineural hearing loss with the ability to perceive sound by stimulating the person's auditory nerve via an array of electrodes implanted in the person's cochlea. FIG. 1 depicts an example cochlear implant. The example cochlear implant includes an external sound processor 101, which is typically worn behind the ear. The cochlear implant has at least one microphone 105 that produces an audio signal 106. Sound processor 101 processes the audio signal 106 to determine an appropriate pattern of electrical stimulation to apply to the recipient of the cochlear implant.
Generally, the pattern of electrical stimulation is determined in accordance with a set of rules referred to as a sound coding strategy. Typically, the sound processor 101 transmits information specifying the desired stimulation pattern over a transcutaneous radio-frequency (RF) link 103 to an implanted stimulator module 102. The implanted stimulator module 102 generates electrical stimuli and delivers those stimuli to an array of electrodes 104, which are implanted in a recipient's cochlea. Electrically stimulating nerves in a cochlea with a cochlear implant may enable persons with sensorineural hearing loss to perceive sound.